Acoustic surface-wave devices

Abstract

An acoustic surface wave device having an interdigital array of parallel electrodes includes a set of four parallel active electrodes spaced apart and with a transverse overlap. The second and third electrodes are aligned. The first and third and second and fourth electrodes are respectively connected together and to corresponding other electrodes of the electrode array.

What is claimed is: 
     
       1. An acoustic surface-wave device comprising a body of piezoelectric material on one surface of which is formed a launching or receiving transducer including an interdigital array of electrodes which includes at least one set of four spaced electrodes, in which set the first and second electrodes are spaced apart along the line of acoustic surface-wave propagation through the transducer and overlap transverse to said propagation line, the third electrode is aligned with the second electrode and is electrically connected in common with the first electrode, and the fourth electrode is spaced apart from the second and third electrodes in said line of propagation, overlaps the third electrode transverse to said propagation line and is electrically connected in common with the second electrode, and means for applying an electric potential to said array of electrodes such that in operation the electrical field between the overlapping third and fourth electrodes has the same direction as the electrical field between the overlapping first and second electrodes. 
     
     
       2. An acoustic surface-wave device as claimed in claim 1, in which the electrodes of the transducer are arranged so that in operation the position along the line of acoustic surface-wave propagation through the transducer where said first electrode is located has a net electric field leaving it (or arriving at it), the position where said second and third electrodes are located has a net electric field arriving at it (or leaving it respectively), and the position where said fourth electrode is located has a net electric field arriving at it (or leaving it respectively). 
     
     
       3. An acoustic surface wave device comprising a substrate composed of piezoelectric material adapted to propagate acoustic surface wave energy, an electromechanical transducer supported on one surface of the substrate and including an array of parallel spaced apart conductive electrodes alternate ones of which are electrically connected to form an interdigitated electrode array with a transverse overlap between at least some of the adjacent electrodes along the longitudinal direction of the array, said array of electrodes including a set of four consecutive parallel electrodes in which the first and second electrodes are spaced apart in the longitudinal direction with a transverse overlap, the third electrode is colinear with the second electrode and is electrically connected to the first electrode and the fourth electrode is electrically connected to the second electrode and is spaced apart from the second and third electrodes in the longitudinal direction and overlaps the third electrode in the transverse direction, and means for applying an electric potential to said array of electrodes. 
     
     
       4. An acoustic surface wave device as claimed in claim 3 wherein at least some of the electrodes of the electrode array are disposed so that the amount of transverse overlap between adjacent electrodes varies along the longitudinal direction of the array. 
     
     
       5. An acoustic surface wave device as claimed in claim 4 further comprising a second set of four consecutive parallel electrodes in which the third and fourth electrodes of the first set of electrodes constitute the first and second electrodes of the second set of electrodes, the third electrode of the second set is colinear with the second electrode of the second set and is electrically connected to the first electrode of the second set, and the fourth electrode of the second set is electrically connected to the second electrode of the second set and is spaded apart from said second set second and third electrodes in the longitudinal direction and overlaps the second set third electrode in the transverse direction. 
     
     
       6. An acoustic surface wave device as claimed in claim 3 further comprising a second set of four consecutive parallel electrodes in which the third and fourth electrodes of the first set of electrodes constitute the first and second electrodes of the second set of electrodes, the third electrode of the second set is colinear with the second electrode of the second set and is electrically connected to the first electrode of the second set, and the fourth electrode of the second set is electrically connected to the second electrode of the second set and is spaded apart from said second set second and third electrodes in the longitudinal directions and overlaps the second set third electrode in the transverse direction. 
     
     
       7. An acoustic surface wave device as claimed in claim 3 further comprising a second set of four consecutive parallel electrodes in which the fourth electrode of the first set constitutes the first electrode of the second set of electrodes, the third electrode of the second set is colinear with the second electrode of the second set and is electrically connected to the first electrode of the second set, and the fourth electrode of the second set is electrically connected to the second electrode of the second set and is spaced apart from said second set second and third electrodes in the longitudinal direction and overlaps the second set third electrode in the transverse direction.